A fixed-layout publication is one where each page has a fixed size (height and width) and the content is precisely laid out at specific locations. Fixed layouts are commonly created using images, but can also be achieved in HTML. They are typically used to create comics, manga, children’s story books, cookbooks and textbooks, but can be found in any material trying to reproduce pixel-precise (or pixel-perfect) layouts, which means the layout design of all elements are in perfect alignment and the website looks exactly the same on all devices, without a single change.
The use of fixed layouts presents a number of challenges for accessibility. For example, the use of images typically limits access to the text. In the same way, changes made to the default fonts and zooming of a page can lead to excessive scrolling or text to be cut off entirely. Content spread across two pages can lose all meaning when only half the information is available at any given time.
Some other difficulties that arise when attempting to make fixed-layout documents accessible include:
Non-text content such as image-based fixed layouts like comics, illustrations and manga are difficult to convert to accessible form because alternative text and descriptions cannot always capture all of the story conveyed through the images. A separate serialization of the story is often required, making it cumbersome and repetitive.
Meaningful sequences are difficult because content elements can be visually placed wherever needed and care is not always taken to ensure that a logical sequence is maintained in the markup. When an assistive technology reads in order of appearance, information and dialogue are rendered out of sequence and become meaningless and confusing.
In the case where content is laid out over two pages, ( a two-page spread) the logical sequence may require a visual reader to move back and forth from page to page. This type of sequence cannot be represented in the markup. Fixed-layout pages are usually designed to be rendered in a specific orientation, and authors may indicate that reading systems should only render the content in that orientation. Users are typically prevented by reading systems from changing the fonts of fixed-layout publications to ensure the content is rendered how the author designed it.
Due to the fixed dimensions of a fixed-layout page, the zoom requirement of this success criterion typically results in the user having to scroll in all directions to read the content.
Even if users are allowed to change the appearance of a page, adding spacing can force text to exceed the boundaries of its container element and/or page. In this case, the overflow text is often hidden from sight.
Bottom line: Try to avoid the use of fixed layouts when content has to be broadly accessible. W3.org has good information about fixed-layout documents, although a lot of it is very technical.